The present invention relates to semiconductor processing, and, more particularly, to planarizing or polishing semiconductor wafer surfaces during the manufacture of integrated circuits.
Semiconductor devices, also called integrated circuits, are mass produced by fabricating of identical circuit patterns on a single semiconductor wafer. During the process, the wafer is cut into identical dies or chips. Although commonly referred to as semiconductor devices, the devices are fabricated from various materials, including conductors (e.g. copper, aluminum and tungsten), non-conductors (e.g. silicon dioxide) and semiconductors (e.g. silicon). Silicon is the most commonly used semiconductor, and is used in either its single crystal or polycrystalline form. Polycrystalline silicon is often referred to as polysilicon or xe2x80x9cpolyxe2x80x9d. The conductivity of the silicon is adjusted by adding impurities in a process commonly referred to as doping.
Within an integrated circuit, thousands of devices (e.g., transistors, diodes) are formed. Typically, contacts are formed where a device interfaces to an area of doped silicon. Specifically, plugs are typically formed to connect metal layers with device active regions. Vias are typically formed to connect metal layers with other metal layers. Also interconnects are typically formed to serve as wiring lines to interconnect the many devices on the integrated circuit and the many regions within an individual device. These contacts and interconnects are formed using conductive materials.
The integrated circuit devices with their various conductive layers, semiconductive layers, insulating layers, contacts and interconnects are formed by fabrication processes, including doping processes, deposition processes, photolithographic processes, etching processes and other processes. At certain steps, it is often desirable to achieve a pre-determined level of surface planarity, uniformity, and/or roughness. It is also desirable to minimize surface defects such as pits and scratches. Such surface irregularities may affect the performance of the final semiconductor device and/or create problems during subsequent processing steps.
One common technique to planarize a wafer is known as chemical mechanical polishing (CMP). CMP is very widely used technique which delivers a slurry of material to the wafer surface and while a polishing pad or belt is passed over the wafer surface. The slurry typically includes a plurality of abrasive particles dispersed in a liquid. For example, U.S. Pat. No. 5,728,308 entitled xe2x80x9cMethod of polishing a semiconductor substrate during production of a semiconductor devicexe2x80x9d discloses a conventional slurry used for chemical mechanical polishing including particulates comprised of metal oxides such as silica (SiO2), alumina (Al2O3), titanium oxide (TiO2), and cerium oxide (CeO2) of a particle size of about 10 nm in an aqueous solution of potassium hydroxide (KOH).
A problem with current CMP slurries is that polished metal in the slurry can cause scratches on the wafer surface or contaminate layers on the wafer. Therefore, the slurry is not re-usable and increases waste.
In view of the foregoing background, it is therefore an object of the present invention to remove metal particles from a slurry during CMP to avoid damaging and/or contaminating the semiconductor wafer.
It is another object of the present invention to provide a slurry which can be processed and re-used during CMP.
These and other objects, features and advantages in accordance with the present invention are provided by a CMP slurry comprising a first emulsion including a continuous aqueous phase and a second emulsion. The first emulsion includes abrasive particles, and the second emulsion captures metal particles polished from the semiconductor wafer. Thus, metal particles can be removed from the slurry during CMP to avoid damaging and/or contaminating the semiconductor wafer. Preferably, the second emulsion comprises an organic phase and a dispersed aqueous phase, and the dispersed aqueous phase preferably comprises a dispersed aqueous acidic phase. The organic phase may comprise at least one of an alcohol and an iso-alcohol and preferably includes at least one complexing agent, such as ethylene diamine tetra-acetate (edta), di-ethylene triamine penta-acidic acid (dtpa), 8-hydroxy quinoline, bi-pyridine, or ortho-phenanthroline, for example, for reacting with metal particles polished from the semiconductor wafer to form organometallic complexes.
The organic phase preferably transports the organometallic complexes to an interface between the organic phase and the dispersed aqueous phase by diffusion. The organometallic complexes may decompose at the interface to release the complexing agent into the organic phase and release the metal particles into the dispersed aqueous phase.
The objects, features and advantages in accordance with the present invention are also provided by a method of making a CMP slurry including the steps of: forming a second emulsion to capture metal particles polished from the semiconductor wafer, emulsifying the second emulsion in a continuous aqueous phase to define a first emulsion, and adding abrasive particles to the continuous aqueous phase. Preferably, the step of forming the second emulsion comprises emulsifying a dispersed aqueous phase in an organic phase. Thus, metal particles can be removed from the slurry during CMP to avoid damaging and/or contaminating the semiconductor wafer.